1. Technical Field of the Invention
The present invention relates to a waste water treatment method and apparatus for biologically treating high-concentration organic waste water, and especially waste water containing fluorine discharged from semiconductor factories and liquid crystal factories.
2. Description of Related Art
From the standpoint of the Water Pollution Prevention Law in Japan, it is necessary to treat waste water containing organic matters at high concentration and also containing metal ions or non-metal ions such as fluorine until metal and non-metal ions and organic matters contained therein reach specified concentrations.
Fluorine-containing high-concentration organic waste water hitherto has been treated as follows in the semiconductor factories or the like when the concentration of fluorine contained in the high-concentration organic waste water is as high as 50-100 ppm and the concentration of TOC (total organic carbon) contained therein is also as high as 2000 ppm or more.
The easiest method of treating such fluorine-containing high-concentration organic waste water is to leave the disposal thereof to an industrial waste collector for incineration. In this case, organic matters in the waste water can be disposed easily by incineration. But it is necessary to use chemical agents to chemically treat the fluorine contained in waste gas generated as a result of the incineration. Accordingly, in addition to incineration equipment, equipment for chemically treating the fluorine contained in the waste gas is required. Thus, the treatment system has a complicated construction and in addition, initial and running costs thereof are considerably high.
As another method of treating the fluorine-containing high-concentration organic waste water, it is treated not by incineration but by, initially, a chemical treatment to remove fluorine contained therein and then, diluting the waste water until its concentration becomes so low as to allow a treatment with microorganisms so that organic matters remaining in the waste water are treated. In another treatment method, process steps are carried out in the order opposite to the above method. Initially, the waste water is diluted until its concentration becomes so low as to allow the waste water to be treated with microorganisms, and then organic matters contained therein are treated. After that, fluorine contained in the waste water is chemically treated with slaked lime, calcium carbonate mineral or the like.
On the other hand, apparatuses and methods of treating fluorine waste water which contains organic matters not at a high concentration but at about tens of parts per million (ppm), are known from Japanese Laid-Open Patent Publication No. 5-4090 and Japanese Laid-Open Patent Publication No. 6-343974.
Herein, waster water containing fluorine at 40-100 ppm and organic matters at 2,000-3,000 ppm in TOC concentration is referred to as "fluorine-containing high-concentration organic waste water", and waste water containing fluorine at 30-300 ppm and organic matters at as low as 10-30 ppm in TOC concentration is referred to as "organic matter-containing fluorine waste water".
In the waste water treatment methods disclosed in the Japanese Laid-Open Patent Publication Nos. 5-4090 and 6-343974, waste water is chemically treated first to reduce fluorine and then organic matters contained in the waste water are treated by microorganisms. Both methods are intended for waste water containing organic matters at as small as less than 100 ppm in TOC concentration.
More specifically, in the method disclosed in Japanese Laid-Open Patent Publication No. 5-4090, as shown in FIG. 15 illustrating a system for carrying out the method, a water-soluble calcium compound is added to waste water to be treated in a coagulation and settlement tank 219 to form calcium fluoride, which is then settled. Then, pH of a supernatant liquid is adjusted to 6.5-7.0 in a pH-adjusting tank 220, and then, in an aeration tank 221, through the aeration treatment, the waste water is allowed to contact pellets, to which microorganisms are fixed, to thereby remove BOD (Biochemical Oxygen Demand) components. Then, a coagulation agent or flocculant is added to the waste water in another coagulation and settlement tank 222 to precipitate a remnant fluorine compound along with microorganisms which have leaked out from the pellets.
On the other hand, in the method disclosed in Japanese Laid-Open Patent Publication No. 6-343974, which uses a system shown in FIG. 16, initially, in a first water tank 301 which is filled with a calcium carbonate mineral 307, waste water containing fluorine and the calcium carbonate mineral 307 are allowed to chemically react with each other. Next, in a second water tank 302 which is also filled with calcium carbonate mineral 307, organic matters contained in the waste water are biologically treated by microorganisms propagating on the calcium carbonate mineral 307.
In semiconductor factories manufacturing integrated circuits, technological innovation is made day after day. Because of the use of new chemical agents, waste waters having properties quite different from those of the conventional ones appear. More specifically, a new chemical agent has been developed for use in post-treatment of aluminum wiring etching. The use of that chemical agent causes waste water to contain a mixture of fluorine and high-concentration organic matters.
The chemical agent has a fluorine compound concentration of about 10,000 ppm and a TOC concentration of about 248,000 ppm. The chemical agent is diluted 100 fold with pure water and then drained. That is, the fluorine concentration of the resulting waste water is about 100 ppm, and the TOC concentration thereof is 2,000-3,000 ppm.
In treating such waste water containing fluorine and high-concentration organic matters, the following two methods are conceivable:
(1) Method of leaving the disposal of waste water to industrial waste collector; and
(2) Method of chemically and biologically treating waste water.
In the method (1) of leaving the disposal of waste water to an industrial waste collector, in addition to the incineration of waste water, fluorine contained in waste gas must be treated with a chemical agent, as described above. Thus, in addition to incineration equipment, the method requires equipment for chemically treating the fluorine contained in the waste gas. Thus, initial and running costs thereof are considerably high. Further, with this method, waste produced by factories may increase, which does not meet the requirements of the times to reduce waste to be disposed of. Therefore, there is a growing demand for the development of a method that allows factories to easily treat waste water by themselves without increasing the amount of waste.
In the method (2) of chemically and biologically treating waste water, it is possible to reduce the amount of waste. But it is necessary to chemically treat the fluorine with slaked lime or calcium carbonate and in addition, biologically treat high-concentration organic matters by active slurry method or the like. This method, which must dilute the waste water containing the organic matters at a high concentration for the biological treatment, requires treating equipment of complicated construction. Further, the initial cost of the treating equipment and the running cost, e.g., for electricity consumed by a blower, a pump or the like are expensive.